The present invention relates to electronic control circuits in general, and more particularly to a monolithically integrated, polarity-reversal protected circuit including at least one transistor stage for switching a resistive load on and off.
There are already known polarity-reversal protected circuits which incorporate a switching transistor and a diode included in the output of the switching transistor. The base of the switching transistor is connected with a control circuit which opens and closes the switching transistor, depending on the requirements. The collector-emitter path of the switching transistor and the diode connect the respective output or connecting terminals which are also connected with one another, for instance by a series connection of an incadescent light bulb and a battery. If the polarity of the battery is inadvertently revesed in this known construction, the diode arranged in the output of the switching transistor becomes non-conductive. Now, if this diode were implemented in a monolithically integrated circuit as a collector-base diode, then a maximum voltage corresponding to the collector-base breakdown voltage could be blocked with this diode. In the event, however, that the battery is connected with correct polarity and the switching transistor is blocked or rendered non-conductive, only a maximum voltage corresponding to the collector-emitter breakdown voltage of the switching transitor can be blocked by this circuit arrangement, and it is well known that this collector-emitter breakdown voltage of the switching transistor is considerably lower than the collector-base breakdown voltage. There are presently not known any monolithically integrated transistor switching stages,especially for the use in motor vehicles where high voltage peaks can occur in the on-board network, which would be securely protected both against high voltage pulses and polarity reversal.